Thin film photovoltaic (PV) modules (also referred to as “solar panels”) are gaining wide acceptance and interest in the industry. The PV modules are conventionally formed by deposition of various semiconductor materials and electrode layers as thin (generally recognized in the art as less than 10 microns) film layers on a glass substrate. The substrate then undergoes various processing steps, including laser scribing processes, to define and isolate individual cells, define a perimeter edge zone around the cells, and to connect the cells in series. These steps result in generation of a plurality of individual solar cells defined within the physical edges of the substrate.
A well known method for collecting the charge from a PV module is to attach a strip of insulation (e.g., an insulating tape) lengthwise along the module across the cells. A conductive foil (e.g. a foil tape or ribbon) is then aligned and attached to the insulation tape. Bus bars (typically in the form of an adhesive bus tape) are then attached at opposite longitudinal ends of the module aligned with the first and last cells, respectively. The bus tapes cross over and attach to the foil layer, collect the charge from the cells, and transfer the charge to the foil ribbon. The foil ribbon is separated in a junction box wherein leads are connected to the separated foil ends. The leads provide a means to connect the PV module to a load, other cells, a grid, and so forth.
The electrical junction between the bus tapes and foil ribbon is critical to the PV module. If the junction fails at either location, an open circuit is created and the PV module becomes useless. Unfortunately, this junction has proven to be problematic. The bus tapes are typically embossed and include a non-conductive adhesive applied to the tape. Electrical contact between the bus tapes and foil ribbon is thus dependent on sufficient ridge depth created by the embossment process. The adhesive is intended to secure the tape to the foil ribbon, but the ridges must penetrate through the adhesive to make electrical contact with the foil ribbon. If the ridge depth is insufficient or the ridges become crushed in the application process, electrical contact is not made or is unreliable. In addition, failure of the adhesive results in the tape pulling away from the foil ribbon, again resulting in loss of electrical contact. This is a particular concern with repeated temperature cycling of the module.
Accordingly, there exists an ongoing need in the industry for an improved, robust, and more reliable electrical contact between the bus tapes and foil ribbon that will reduce the occurrence of failed PV modules.